The present invention relates to an auxiliary drive mechanism for propelling a boat in the event of failure of a main engine or transmission.
It is common for motor-powered boats to provide an auxiliary drive mechanism for propelling the boat if there should occur a failure of the main engine or the transmission. Auxiliary drive mechanisms now available are often called xe2x80x9cget home drivesxe2x80x9d and are usually powered by an auxiliary power unit such as an engine driven generator. The means of power are either from the electricity produced by the generator or through hydraulics such as by an auxiliary hydraulic pump mounted to the generator""s engine. The main function of the auxiliary drive unit is to rotate the propeller shaft, usually at a reduced speed, but sufficient to propel the boat to port. The usual method of attaching the auxiliary drive mechanism to the propeller shaft involves the use of belts, chains, or gears which must be disengaged during periods when the propeller shaft is being driven by the main engine to avoid being subjected excessive wear.
A drive connection between the auxiliary motor and the propeller shaft can be achieved by the use of a manually attachable belt or chain interconnecting the auxiliary motor (mounted to the boat hull) and a pulley or sprocket affixed to the propeller shaft. Alternatively, gearing could be used to transmit the drive fro the auxiliary motor to a gear affixed to the propeller shaft, wherein gears sets are manually rotated into meshing engagement.
The need to make the connection of the drive linkage manually is inconvenient. Moreover, in order to perform the task, it is necessary for an operator to enter the engine room, which can be difficult if the boat is still moving through the water, because the propeller will be turning the propeller shaft.
Additional shortcomings include the need to keep the belts, chains or gears in alignment as the engine mounts, the engine beds, and the shaft bearing undergo wear. Moreover, with the auxiliary motor attached the boat hull, the transmission of power via chains, belts or gears will result in the application of a side load to the propeller shaft, due to the pull of the belt or chain, or the push of the gears. Such side thrust can be effectively resisted by arranging an additional bearing on the propeller shaft, but this adds to the expense and complexity of the mechanism. Also, the bearing will be in constant rotation when the propeller shaft is rotating, and thus constitutes another part which will wear out and require replacement.
Auxiliary drive mechanisms have been proposed which can be automatically engaged, e.g., by means of a clutch mechanism. For example, U.S. Pat. No. 6,033,271 discloses an auxiliary drive for a propeller shaft 4 which includes an electric motor 42 mounted to the boat hull and connected by way of a clutch 43 to a transmission 5. The transmission 5 is connected to a cogwheel 6 which is mounted on a sleeve 7 arranged coaxially with the propeller shaft 4. The sleeve 7 engages a clutch 8 which is connected to the propeller shaft 4 by means of a flange 9. Such a mechanism involves the use of a expensive clutch mechanisms and may impart a an undesirable side thrust to the propeller shaft.
It would be desirable to provide an auxiliary drive mechanism which does not impart a side thrust to the propeller shaft.
It would also be desirable to provide such a mechanism can be mechanically activated and which has no need of a clutch.
One aspect of the present invention involves a boat drive system which includes a transmission unit adapted to be mounted to a boat hull. A propeller shaft is connected to the transmission unit to be driven thereby. A coupling member is mounted coaxially with the propeller shaft for rotation therewith and includes a first rotation transmission structure disposed on an end of the coupling member facing away from the transmission unit. An auxiliary drive unit is provided for driving the propeller shaft. The auxiliary drive unit includes a housing mounted for movement relative to the transmission unit in a direction parallel to a longitudinal axis of the propeller shaft. An auxiliary motor is mounted on the housing. A drive wheel is rotatably mounted to the housing and is operably connected to the auxiliary motor to be driven thereby. The drive wheel is hollow, with the propeller shaft extending therethrough. The drive wheel includes a second rotation transmission structure facing the first rotation transmission structure. An actuating mechanism is provided for moving the auxiliary unit in a direction parallel to the axis selectively toward and away from the transmission unit, to bring the first and second rotation transmitting structures into and out of rotation transmitting connection.
The invention also pertains to the auxiliary drive unit itself. The auxiliary drive unit includes a housing having first and second end walls interconnected by a sidewall. An auxiliary motor is attached to the exterior of the first end wall adjacent an upper end thereof. The motor includes a motor shaft extending into the housing. A drive wheel is disposed at a lower end of the housing and extends between the first and second end walls and is mounted therein for rotation about an axis oriented parallel to the motor shaft. The drive wheel is hollow and includes an axial end having an annular row of axially facing teeth arranged around the axis of the drive wheel. A power transfer mechanism interconnects the motor shaft and the drive wheel.